1. Technical Field
The present disclosure relates to advantageous seal systems having sequentially engageable seals, and more particularly to replacement seal systems that provide sequential engagement of lip seal members with moving element(s), e.g., rotating and/or reciprocating shafts, through relative movement between a barrier member and the lip seal members.
2. Background Art
A sealing apparatus or seal cartridge is generally used in a fluid-handling machine to seal a case or body of the machine around a rotating or reciprocating shaft that penetrates the case or body. The sealing apparatus typically includes a lip seal mounted to a stationary housing or gland. The gland is bolted to the case or body of the machine. The lip seal extends radially from the housing to be pressed against the rotating or reciprocating circumference of the shaft, or to a shaft sleeve fixed to the shaft. Such a sealing apparatus is used, for example, at the penetration of a shaft into a pump case to prevent the leakage of pumped process fluid around the joint formed by the shaft penetration.
In operation, lips seals have a limited useful life due to wear. At the end of the useful life, leakage will develop at the interface between the stationary lip seal and the rotating/reciprocating shaft. When leakage is observed, the operation of the fluid handling machine generally must be terminated and the sealing apparatus must be at least partially dismantled to replace the lip seal. Such dismantling and maintenance is time consuming and expensive. Additionally, there is the possibility that a significant cost in operating downtime may be suffered due to the replacement of the lip seal.
Various approaches have been undertaken to improve the performance of sealing apparatus and/or to lengthen service periods between required maintenance. Thus, for example, U.S. Pat. No. 2,836,441 to Doble discloses a shaft seal system in which the shaft includes a conical surface and the seal is axially repositionable along the shaft to achieve improved engagement between the seal and the shaft as the system experiences wear. In U.S. Pat. No. 3,698,724 to Blachere et al., a sealing device is disclosed that includes a series of inflatable seals positioned in grooves. As individual inflatable seals fail, they are moved out of engagement with the shaft and replaced, while the remaining inflatable seals provide the required sealing function.
Efforts have also been directed to developing sealing apparatus that include multiple seal members that are brought into contact with a shaft at different points in time, e.g., as individual seal members are worn down or fail. For example, U.S. Pat. No. 3,727,923 to McEwen provides a “double life” seal system in which a garter spring is repositioned from a first position, where it biases a first seal into engagement with a shaft, to a second position where a second, axially spaced seal is biased into engagement with the shaft. The McEwen '923 provides a system for automatically moving the garter spring from the first position to the second position after a predetermined level of wear.
The patent literature also includes several seal systems in which two or more seal members are axially spaced along a shaft, and individual seal members are axially repositioned so as to be brought into contact with the shaft at appropriate points in time. U.S. Pat. No. 3,773,336 to Walter et al. discloses a seal system in which a spare seal member is initially positioned adjacent a recess in the shaft (or is associated bushing), thereby avoiding engagement with the shaft until needed/desired. The spare seal member may be brought into contact with the shaft by axially repositioning the seal holder or the shaft/bushing. Similarly, U.S. Pat. No. 4,008,897 to Wentworth provides a reserve sealing ring that initially extends into an annular chamber, i.e., is not engaged with the shaft. Axial repositioning of the reserve sealingring to effect engagement with the shaft is accomplished through an hydraulically pressurized system.
U.S. Pat. Nos. 5,820,132, 6,098,990 and 6,152,454 to Marnot also describe seal systems in which a spare seal is initially positioned adjacent a set back region formed in the shaft. As the spare seal is axially repositioned so as to be brought into engagement with the shaft, e.g., using a screw jack or fluid-pressure annular jack, the replaced seal is moved adjacent a set back region formed in the shaft, i.e., out of engagement with the shaft. The Marnot patents further contemplate a control system in which a leak detector monitors system operation and causes the spare seal to move into engagement with the shaft (or signals an operator who can manually cause the spare seal to move into engagement with the shaft).
Despite efforts to date, a need remains for seal system designs that provide reliable, efficacious sealing functionality, that extend periods of useful operation, and that minimize maintenance downtime. Moreover, a need remains for seal system designs that achieve improved system operation and functionality over the course of a use cycle. These and other needs are satisfied by the sealing systems disclosed herein.